Theoretical studies on D-A-π-A and D-(A-π-A)2 dyes with thiophene-based acceptor for high performance p-type dye-sensitized solar cells

Abstract

Eight p-type dyes with D-A-π-A or D-(A-π-A)2 structures were designed to investigate the effect of thiophene derivatives acting as acceptors on the properties of the sensitizers. Structure optimizations were performed by the density functional theory (DFT) method, and the electronic and absorption characters were obtained with the time-dependent DFT (TD-DFT). The results show that all the eight dyes have an excellent light harvesting efficiency (LHE) performance (0.99–1.00). And the driving forces of hole injection (ΔGinj) and dye regeneration (ΔGreg) of all dyes are more negative than −0.2 eV, resulting in an efficient hole injection and dye regeneration. Furthermore, the dyes with 2,3-dimethylpyrazine thiophene moiety (DMPZT-1) have the narrowest energy gaps. Importantly, the dyes with DMPZT-1 moiety display red shifts of the UV–vis absorption and enhanced absorptions of visible light (400–800 nm) in comparison to their prototype. In addition, the charge recombination (ΔGCR) performance of A1 and B1 is improved by DMPZT-1. Compared with the D-A-π-A dyes, the additional -A-π-A chain in D-(A-π-A)2 could decrease energy gap further and improve the visible light adsorption, LHE, and driving forces for hole injection and charge regeneration (ΔGinj and ΔGreg). Replacing thiophene with DMPZT-1 acceptor is an effective way to improve the performance of the dyes.